Preheat the oven to 300 degrees F (150 degrees C).
In a medium bowl, mix together the ground beef, bread crumbs, cayenne pepper, paprika, onion powder, garlic powder, ground black pepper, and salt. Press into an 8x8 inch square baking dish, or casserole dish.
Bake for 2 hours in the preheated oven, until cooked through. Set aside to cool for at least 1/2 hour, the meat will slice even better if it is actually chilled completely.
To make the sauce, combine the evaporated milk, sugar and vinegar in a jar with a lid, and shake well to blend. Set aside to thicken.
Heat a large skillet over medium-high heat, and slice off thin slices of the meat loaf. Fry the slices briefly in the hot skillet, until browned on each side.
Remove from the skillet, and keep warm. Flick a little water onto the hot skillet, and brown the pita breads a little on each side to soften.
Load up one side of pitas with meat slices, tomatoes and onion. Spoon sauce over the filling, and fold pitas in half, then towards the center. Voila, you're eating!
